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Wave overtopping on gentle slope seawalls for both smooth and stepped front faces was investigated in a laboratory wave flume. Overtopping rates were measured by a catchment basin placed behind the seawall. Overtopping velocity and water depth at the top of the seawall were simultaneously measured by using a Laser Doppler Velocimeter and a wave gage. It was found that the velocity of overtopping water has a sharp peak just after initiation of each overtopping event. The water depth on the seawall crown shows relatively gradual decrease.

A numerical model of three-dimensional Large Eddy Simulation was developed for evaluating the instantaneous overtopping discharge and compared to the experimental results. The calculated root-mean-square value of water surface elevation at the toe of the seawall agreed very well with the measured value, but large discrepancies were found for individual wave deformation in some waves. The magnitude of the calculated velocity on the top of seawall was generally smaller than that of the measured velocity. The calculated volume of the overtopping water was between the volumes measured for the smooth seawall and the stepped seawall. Since the two-dimensional Large Eddy Simulation model far overestimated the overtopping volume, it was considered that appropriate representation of three-dimensional large eddies generated by wave breaking is important for wave overtopping evaluation.

A particle method, or a gridless Lagrangian method, shows the high performance in describing the complicated behavior of water surface with the fragmentation and coalescence of water. In this paper, a wave overtopping process on a vertical seawall is numerically simulated on the basis of the Navier–Stokes equation with surface-tension term, which is discretized by the MPS (moving particle semi-implicit) method belonging to the category of the particle method. An improvement of the listing process of neighboring particle is introduced to reduce the computational load. Wave overtopping process in the experiments are well reproduced by the MPS method. The predictions of the MPS method of the overtopping volume agree well with the experimental results.

To increase physical insight into wave overwash processes at low-crested beach barriers, wave overtopping discharge events rather than the conventional average overtopping discharge need to be quantified. Also, in order to make intelligent use of the many empirical formulations on wave overtopping discharge at breakwaters from literature, a single-valued appropriate slope for a natural beach needs to be derived. To resolve these issues, laboratory experiments of composite-slope low-crested barriers were carried out. The tests deal with overwash on a smooth non-uniform slope on shallow foreshores.

The conventional average overtopping discharge concept does not represent the discontinuous character and associated strength of overtopping flow. Instead, e.g. for purposes of morphological modeling, wave overtopping should be treated as an event-based process. In this study, several new parameters such as the wave-averaged overtopping time, the relative total overtopping time, the overtopping asymmetry, the average maximum discharge and the average instantaneous discharge are defined and formulated.

A new approach for defining an equivalent slope is proposed in the parameterization of the overtopping discharge that also takes into account effects of the wave period. It is experimentally shown to be an improvement over the conventional approach by Van der Meer [1998], especially eligible for low-crested sandy slopes such as barriers, dikes, dunes, etc on shallow foreshores.

This paper analyses the influence on the measured mean overtopping discharge of the duration of physical model tests of wave overtopping, bearing in mind the practical purpose of the studies, and the required accuracy of the measurements. The case study of the South Breakwater of Póvoa de Varzim Harbor, Portugal, is used to investigate this subject. During the two-dimensional physical model tests, three main target test conditions were used. For each one, different wave trains were utilized, all conforming to the same target JONSWAP spectrum, and three different test durations were employed. The number of random waves ranged from about 300 to 2400. Then, one of the three main test conditions was again used, but for twelve different test durations. In this case, the number of waves ranged from about 150 to 1900.

The results suggest that the convergence of the mean overtopping discharge to a constant value with increasing test duration is not obvious. Regardless of the test duration, the information obtained with a single test gives limited information about the expected mean discharge, as the mean overtopping discharge varies even for the same wave and structure characteristics. Consequently, more information is obtained on the mean discharge if several tests of the same short duration (but with different time series) are undertaken rather than if one test of long duration is carried out.

Extensive laboratory experiments were carried out to investigate the efficiency of low (vertical) crown-walls on the reduction of wave overtopping on sea-dikes. It is shown that the reduction of wave overtopping discharge by crown-walls is inadequately described in the TAW-2002 guidelines. A new approach for the wall influence has therefore been developed, explicitly taking into account both the wall height and the promenade width. The approach can straightforwardly be incorporated in the original formulations of TAW-2002 to significantly improve the prediction of wave overtopping on sea-dikes crowned with this type of walls.

Little is known about the strength of the land-side slopes of the Vietnamese sea dikes under overtopping attack. Some grass-covered slopes were tested by a wave overtopping simulator. The paper describes the simulator and presents the test results. The tested grass covers could withstand overtopping rates varying from 20 l/s to 100 l/s per meter of dike length in some hours. Damage usually started at bare spots, at the transition between the slope and the toe, at the transition between different materials, and around objects (e.g. big trees). These features reduce the strength of a grass cover and therefore should be avoided.

Crown heights of seawalls should be designed to suppress overtopping discharge to a permissible level. The permissible level is determined from viewpoints of the structure types of coastal seawalls and hinterland use. It is usually difficult to design the crown heights of seawalls, especially in the present time where climate change due to global warming is expected. This study analyzes climate change effects such as sea level rise (SLR) and increase of waves and surges on the failure probability of seawalls under various conditions of crown height, toe depth and slope by using a Level III reliability analysis. It was found that the difference of SLR trends (fast, medium or low) has less impact on overtopping rates than the differences in wave height change for a seawall at a target location.

This contribution presents a new Artificial Neural Network (ANN) tool that is able to predict the main parameters describing the wave-structure interaction processes: the mean wave overtopping discharge ($q$), the wave transmission and wave reflection coefficients ($K_t$ and $K_r$). This ANN tool is trained on an extended database (based on the CLASH database) of physical model tests, including at least one of the three output parameters, for a total number of nearly 18,000 tests. The selected 15 nondimensional ANN input parameters represent the most significant effects of the structure type (geometry, amour size and roughness) and of the wave attack (wave steepness, breaking, shoaling, wave obliquity). The model can be used for design purposes, leading to a greater accuracy than existing formulae and similar tools for complex geometries for the prediction of $K_r$ and $K_t$, and it has a similar accuracy as the CLASH ANN for predicting $q$.

Single layer concrete armor systems are being widely used nowadays in the design of rubble mound breakwaters. Recently, a new concrete armor unit has been developed and applied as single layer armor system in the repair works of one damaged breakwater at Al Fujeirah, UAE. It has a symmetrical shape, in contrast to most other units. Modern single layer concrete armor units that exist at this moment have design guidelines in terms of placement, stability and overtopping. However, because of lack of laboratory research and the little experience of using Crablock, no design guidance exists yet for this new single layer block compared to other existing one layer units. Being a new armor unit, the placement was investigated first. Then physical model tests were performed in a wave flume to come up with results on stability and wave overtopping. Furthermore, to determine the interlocking properties of armor units, pull tests were also conducted in this research. The placement tests showed that uniform placement was best achieved with a rectangular grid on a relatively small underlayer of rock. Test results on stability showed that longer waves affected the armor layer a little more, with more rocking and earlier start of damage. Packing density as well as placement pattern showed no influence on wave overtopping. The overtopping tests gave larger overtopping than expected, which might be due to the fairly steep 1:30 foreshore that gave a large ratio of significant wave-height from the time domain and the spectral wave-height.

In the recent years, various geo-synthetic components find an extensive application in civil and coastal engineering practice. Commonly, geo-synthetics have a wide application for secondary or tertiary purposes, such as filtration, separation, barrier, reinforcement, whereas, they can be potentially exploited for various other applications in the coastal engineering practice. A sustainable seawall cross-section comprising different geo-synthetic products was proposed to be erected along the Pallana Beach ($19^{\circ }17^{\prime }55.19^{\prime \prime }$ N and $76^{\circ }23^{\prime }18.55^{\prime \prime }$ E), located in Alleppey district of Kerala along the south-west Indian coastline. Since the subsoil at the location is poorly graded, it was decided to replace the conventional materials like rock boulders and concrete armour units with geo-synthetic products. A comprehensive physical model study was conducted to assess the hydrodynamic performance (i.e. reflection, run-up, and pressure distribution) of the geo-synthetic seawall cross-section for a wide range of random wave characteristics and two water depth conditions. The relative overtopping rates for the seawall at varying water levels are computed conservatively from the guidelines prescribed by the EurOtop Manual and XGB Overtopping model.

Artificial revetments are commonly constructed on reef-flats to protect the rear infrastructure. Evaluating the performance of a revetment under extreme wave conditions requires accurate prediction of wave overtopping. To simulate tsunami wave overtopping on an artificial revetment above a coral reef-flat, a numerical model based on the weakly compressible smoothed particle hydrodynamics (WCSPH) method is developed. This numerical model includes an additional dissipative term in the continuity equation and a dynamic boundary condition enhancement to correct the pressure distortion from particles at the boundary. Reef topography is simplified as a steep reef-face and a horizontal reef-flat, and tsunami waves are described as solitary waves. This research explores the characteristics of solitary wave overtopping on the revetment above the reef-flat with varying slope angles and reef-flat lengths.

The South Pacific Island nation of Tuvalu, which is composed of coral gravel and sand, is vulnerable to storm waves and sea level rise, resulting in beach erosion. Beach nourishment with self-produced coral gravel and sand was implemented in Tuvalu as the first trial of a user- and eco-friendly type of coastal conservation measure in Pacific Island countries. In order to examine the applicability of this type of coastal conservation measure, continuous monitoring has been carried out for one year to check the change in shoreline and beach profile. Beach monitoring for large-scale reclamation project, which was executed at the neighboring coast in almost the same period, was also conducted to compare the change of beach in the two different projects. The results show that the executed gravel beach nourishment can maintain stability under seasonal and extreme condition of wave actions.

Various new types of seawalls have been adopted instead of existing seawalls such as vertical and block mound seawalls, from the comprehensive viewpoints of disaster prevention, coastal environment and utilization. However, a practical estimation procedure for wave overtopping rate of complex-shaped seawalls has not been established yet. The purpose of this study is, therefore, to numerically examine countermeasures against wave overtopping around road revetment in Okinawa Main Island by conducting numerical simulation using a two-dimensional numerical wave flume 'CADMAS-SURF'. As a result, it is revealed that the CADMAS-SURF can represent wave overtopping phenomena at actual fields. Moreover, numerical computations with the CADMAS-SURF are found to be useful in comprehensively discussing the prevention of wave overtopping disaster.